1. Field of the Invention
This invention relates to an axial piston pump capable of reciprocating a piston provided in a cylinder chamber in an axial direction of a drive shaft by using cam device capable of rotating integrally with the drive shaft. The invention also relates to a power transmission device having the axial piston pump.
2. Description of the Related Art
There is a conventional multi-stroke type axial piston pump, which has cam members having cam surfaces facing in an axial direction of a drive shaft and rotating integrally with the drive shaft, and in which roller rolling on the cam surfaces are supported to pistons reciprocating in the axial direction (see Japanese Patent Application Publication No. 2006-233972 (JP-A-2006-233972)).
The shape of each cam surface of the cam member of the pump disclosed in JP-A-2006-233972 is constant, and the pump capacity cannot be changed due to a constant stroke quantity of the pistons. Therefore, the pump disclosed in JP-A-2006-233972 is not suitable for changing the pump capacity depending on the situation.
However, when such a pump is incorporated in an automatic transmission of a vehicle such as an automobile, and the input side and the output side of a power transmission path are connected to a drive shaft and a driven shaft of the pump, respectively, to drive the pump by means of a rotational difference between the input side and the output side, the flow rate of oil suctioned by the pump increases and thereby the suction resistance of the oil increases due to a significant rotational difference between the input side and the output side upon startup from rest, which might impede the rollers from following the cam surface. Therefore, it is desired to change this configuration in accordance with the situation of the pump capacity and prevent the increase of the flow rate of the oil suctioned by the pump.